A multitude of experiments over the past century have yielded insights into cellular and synaptic organization of the microcircuitry of the neocortex and to its possible role as a functional unit—a column of six layers of cells. The available data is, however, highly fragmented and often conflicting. More importantly, the gaps in our knowledge of neocortical column are so large that it would require an impractical number of experiments to fill all of them.
A model of a neuronal circuit may need to account for known features of synaptic connectivity, i.e. the connectome of the local microcircuit. Since there is a vast number of potential classes of synaptic pathways, only a handful have been anatomically characterized. In the context of neuronal circuits, structural connectivity is often different from functional connectivity.